Loxosceles reclusa (the poisonous brown recluse spider) is the causative agent of severe necrotizing wounds embodying aspects of chronicity if not treated. The proteins and toxins of the venom are partially characterized from our previous studies. The dermonecrotoxin can be identified in polyacrylamide gels and Sephadex column eluants by its potent biological activity. We will characterize this component of the venom in terms of its biochemical properties, its toxic activity and mechanism of action and antigenic qualities. A second component of venom which destroys the hemolytic activity of serum complement and which may contribute to the toxic behavior of the venom due to leukotaxic activities will also be studied. A venom hemolysin will also be characterized. It is believed that an understanding of these three venom components will permit the formulation of a theory of lesion development which will lead to a rational therapeutic choice. The passive hemagglutination test for diagnosis of recluse spider bites will be improved.